Kingdom Animalia – Cnidaria corals, sea anemones, jelly fish, box jellies, hydra, sea fans Phylum Cnidaria (~3000 species); general characteristics: Have tissue level of organization, with two tissue layers (diploblastic) Have radial symmetry Have specialized stinging structures called cnidae Have only one opening to the body cavity / digestive cavity Have no head, no centralized nervous system (only a nerve net), no discrete gas exchange, excretory, or circulatory systems Exhibit alternation of asexual polypoid and sexual medusoid generations.

Kingdom Animalia – Cnidaria General body forms 2 body forms: Polyp and Medusa 2 tissue layers (diploblastic), ectoderm to the outside (blue), and endoderm to the inside (yellow). The layer in between is just a jelly-like material called the mesoglea (it is not a true tissue) Only one opening to the gastrovascular cavity acts as mouth and anus

Kingdom Animalia – Cnidaria General body forms Cnidarians have radial symmetry:

Kingdom Animalia – Cnidaria All cnidarians have specialized stinging or adhesive structures called cnidae When triggered, the the cnidocyte cells discharge the cnidae. A specialized form of cnidae called the nematocyst, has a harpoon like structure that enters the flesh of the potential predator or prey, releasing neurotoxins. Discharge acceleration is at 40,000g!!! Need both physical and chemical stimulation to induce release. Why do you think this is?

Kingdom Animalia – Cnidaria No matter what the size or shape of the cnidarian, they all have cnidae, and they are all made up of one or more of polyp or medusoid body forms

Kingdom Animalia – Cnidaria In general, cnidarians alternate between sexual medusoid and asexual polypoid forms There are a lot of exceptions though…

Kingdom Animalia – Platyhelminthes Have tissue level of organization, with three tissue layers (triploblastic – with endoderm, ectoderm, and mesoderm) Have bilateral symmetry Have only one opening to the body cavity / digestive cavity Have cephalization (and at least at some stage of their lives, so will all the animals that we’ll discuss from now on. Are hermaphroditic, with complex reproductive systems Phylum Platyhelminthes – flat worms (~20,000 species); general characteristics: Can be free-living or parasitic Have great regenerative abilities!!!

Kingdom Animalia – Nematoda Phylum nematoda – round worms (~50,000 species, or more?); general characteristics: Very, very, very, very, very, very, common!!! One study found 90,000 nematordes in a single rotting apple. Maybe we’ll check this one out for ourselves in next weeks lab !! Another study found 236 different species in about 6.7 cc of coastal mud!! Triploblastic, bilateral, vermiform, un-segmented, pseudocoelomates Body round in cross section and covered by a layered cuticle; growth in juveniles Usually accompanied by molting Have complete gut Have no specialized circulatory or gas exchange structures, and only longitudinal muscles. Why do you think they need a substrate to live in? Can be free-living or parasitic

Kingdom Animalia – Nematoda Parasitic example: Heart worms… cool eh?

Kingdom Animalia – Nematoda Whereas cnidarians and platyhelminthes did not have a body cavity (coelom), Nematodes do. It is however a pseudocoelom. All the other animals that we discuss from now on will have true coelom (including us!). Can you tell what the difference is between a coelom and a pseudocoelom? What is the advantage of having a coelom?